Some Factors affecting the Viability of Faecal Bacteria in Water

Abstract

SUMMARY: The effect of various conditions on the rate of death of Bacterium coli and of Streptococcus faecalis in dilute buffer solutions was followed by making colony counts at intervals during prolonged periods of incubation and then constructing mortality curves. The form of these curves was characteristic for each organism. Of the pH values investigated (approximately 5, 6, 7 and 8) both organisms were least viable in the range 6 to 7. Strep. faecalis was not affected by the degree of oxygenation of the water but Bad. coli died much more rapidly under anaerobic than under aerobic conditions. Growth of Bact. coli was observed with as little as 0.28 part per million organic matter in solution. A much higher concentration of nutriment was required for growth of Strep. faecalis; with a concentration slightly below that required for growth the viable population remained virtually stable for a long period. The rate of death depended on the age of the cells a t the time of immersion in water.Factors affecting the longevity in water of organisms used as indices of pollution are of importance in the sanitary survey of rivers or in assessing the suitability of water for drinking purposes. Reports in the literature suggest that the period of survival may be conditioned by a number of factors but the conclusions drawn are often open to doubt owing to failure t o arrange for conditions to be the same in comparable experiments. Moreover, in earlier work there is often some doubt of the precise characters of the organism referred to as Bacterium coli. \'ery few observations appear to have been made on the longevity of Streptococcus fa<ecalis. METHODSThe factors studied were pH value, oxygen tension, concentration of nutrient material, and age of culture a t time of immersion in water. I n the investigation of any one factor, precautions were taken to ensure that other Conditions remained constant. Thc strains of bacteria used had all been isolated fro111 sewage or river water arid before use in this work were tested for characteristic reactions. These were : Bact. coli RESl%'FS Form of death curueWhen iiuinbcrs of surviving bacteria, expressed as percentages, were plotted against the periods for which the culture had been suspended in bufler, the form of the curve was usually sigmoid, as in Fig. 1. Such curves approached the horizontal axis so gradually that an exact period of survival could not be estimated. When, however, the percentages of bacteria surviving were replaced by the logarithms of the percentages, the curves approached the horizontal axis much more steepIy, as in Fig. 2. The period of survival was therefore conveniently expressed as the time corresponding to the point of intersection of such a curve with the axis, i.e. the time required for destruction of 99 yo of thc cells originally present.The curves for Bact. coli and Strep. jkecalis were characteristically of difierent shapes, and corresponded to the two principal types of deviation from the logarithmic form discussed by Hinshelwood (1951).With Bact....

Some chemical and bacterial characteristics of bottom deposits from lakes and estuaries

“…They would, however, be affected by several conditions such as pH value, temperature, degree ofoxygenation, and concentration oforganic matter (cf. Allen, Pasley & Pierce, 1952).…”

The survival patterns of selected faecal bacteria in tropical fresh waters

“…Although there have been several investigations into the relative survival characteristics of faecal bacteria in water (e.g. Allen, Pasley & Pierce, 1952;Gyllenberg, Niemela & Sormunen, 1960;Geldreich et al 1968;McFeters et al 1974;Zanoni & Fleissner, 1982), these have often produced differing results. For example, Deaner & Kerri (1969) suggested that re-growth of 'non-faecal' coliforms was common in water, whereas McFeters et al (1974) observed no such growth of coliform organisms in well-water.…”

Comparative Survival of Indicator Bacteria and Enteric Pathogens in Well Water

“…Studies have been performed to compare the survival of the fecal streptococci and the coliform bacteria (1,9,13,14,16). However, in each case either the bacterial populations were not defined or a highly artificial laboratory test system was used.…”